The invention concerns lubricating compositions having improved properties. Another aspect of the invention relates to additive compositions which impart extreme pressure properties to lubricating compositions.
Additives known as extreme pressure agents are employed to increase the load carrying capacity of lubricants. The extreme pressure agents promote the formation of a surface film and thereby prevent wear, welding and abrasion of the contacting surfaces. When used in lubrication of internal combustion engines, the mechanical efficiency enhanced by decreased friction loss further results in decreased fuel consumption and energy savings.
It is known that certain bismuth based compositions possess antifriction properties. U.S. Pat. No. 5,385,683 discloses antifriction compositions composed of bismuth 2-(ethylhexanoate or neodecanoate and a tin compound. Bismuth dithiocarbamate compounds are disclosed as antioxidants in U.S. Pat. No. 2,716,089 and as extreme pressure agents in U.S. Pat. No. 3,139,405. Polyvalent metal carboxylate-coordinated slats of phosphorodithioates as antioxidants are taught by U.S. Pat. No. 3,523,081.
Extreme pressure compositions based on alkylenebisdithiocarbamates are known lubricating additives. U.S. Pat. No. 4,648,985 discloses extreme pressure additive system composed of an alkylenebisdithiocarbamate, copper dithiocarbamate and metal phosphorodithioate.
Surprisingly, it has been now discovered that certain bismuth compounds described therein produce synergistic extreme pressure effect in combination with alkylenebisdithiocarbamates.